With less than 18 months until the International Olympic Committee (IOC) selects the winning host-city at its 2017 Session in the Peruvian capital Lima, I estimate that as much as 20 per cent of the electorate that will ultimately take this decision remains unidentified.

With races for what many regard as the biggest prize in sport generally pretty tight affairs, this is easily enough to have a decisive impact on the outcome of a contest that currently pits the US west-coast city of Los Angeles against the European trio of Budapest, Paris and Rome.

With bid strategists already grappling with the novelties of a reformed system that seems to facilitate much more input from senior IOC administrators at a relatively early stage in the race, this additional layer of uncertainty may be occasioning a certain amount of what an old schoolteacher of mine would have referred to as wailing and gnashing of teeth.

Of course, a small proportion of voters will always be unknown this far out from polling day.

But the relatively low number of current IOC members, at least when compared with the state of affairs for most of the time I have covered the Movement, has combined with the relatively high number who are from countries with candidate-cities and the big influx of new members expected at this year’s Session in Rio to produce this unusually high quotient of mystery voters.

My back-of-envelope calculations are as follows:

The number of IOC members at present is 92.

However, I reckon that only 74 of these are likely to cast ballots in the first round of 2024 voting; that is provided we still have a full quartet of candidate-cities by that point and that the grim reaper has been merciful.

These 18 presumed non-voters may be broken down as follows:

Three – General Mounir Sabet (Egypt), Timothy Fok (Hong Kong) and Issa Hayatou (Cameroon) – will attain their respective age limits during 2016 and should therefore cease to be full IOC members at the end of this year.

As many as nine are from countries with a candidate-city in the race, meaning they would not vote unless and until the city from that country is eliminated.

These are: Italy (3) Franco Carraro, Mario Pescante and Ottavio Cinquanta; Hungary (1) Pál Schmitt; United States (3) Anita DeFrantz, Angela Ruggiero and Larry Probst; and France (2) Guy Drut and Tony Estanguet.

That makes 12.

A further five - Claudia Bokel (Germany), Dae Sung Moon (South Korea), Yumilka Ruíz Luaces (Cuba), Alexander Popov (Russia) and Barbara Kendall (New Zealand) – are IOC Athletes’ Commission members who this year complete what are normally eight-year terms both on the Commission and as IOC members.

The remaining presumed non-voter is IOC President Thomas Bach.

As usual with the Olympic Movement, there are one or two ifs, buts and maybes.

Fok and Hayatou might conceivably receive one-off four-year extensions, so international relations bods on the various bid teams cannot entirely cross them off their lists just yet.

Retiring Athletes’ Commission members can in theory be granted IOC membership in their own right, as it were; Frankie Fredericks, the ex-sprinter from Namibia, was able to make this switch in 2012.

All remaining current IOC members whom I have not mentioned should I think have first-round votes in Lima.

Who will be joining them?

Well, it is much easier to make a decent stab at how many more first-round voters there are likely to be than to name them.

Pretty much all should become clear though by the end of the Rio Session – that is to say a little more than a year before the all-important vote.

There will be four new Athletes’ Commission members and, while we cannot yet say who they will be, we can narrow the possibilities down to just two dozen.

These are the 24 individuals who are standing for election to the four available places by athletes participating in the Rio Games.

Some of these candidates are very prominent athletes indeed; they include Robert Scheidt, the Brazilian sailor, Saina Nehwal, the Indian badminton player, and Luca Scola, the Argentinian basketball player.

This article by insidethegames Editor Duncan Mackay includes the full line-up.

As things stand, however, two of the 24 candidates – Alessandra Sensini and Daniel Gyurta - would not be able to cast first-round votes in the 2024 ballot even if they do become IOC members.

This is because they are from countries, Italy and Hungary respectively, with cities in the race.

This year’s IOC Session is also expected to induct the first large batch of new members since Bach assumed the Presidency in September 2013.

Indications have reached us that the number of newcomers could be at least 10; indeed with a list of "possibles" said to stretch to well over 100 and plenty of headroom available before hitting the 115-member upper limit, let’s take a punt on 12.

This would take the first-round electorate in that 2024 contest to around 90, provided, once again, that none of the newcomers are from countries fielding candidate-cities.

With the field apparently so broad, and the selection process so opaque, there seems very limited usefulness in trying to second-guess who the new members might be, beyond making the following observations:

It would be surprising if Sebastian Coe - now the global figurehead of the bedrock (if troubled) Olympic sport of athletics, and with an Olympic CV that few in any era could match - does not finally make it into sport’s most powerful club.

It would be remarkable if there were no new member from the Ancient Olympic cradle of Greece; I am led to believe that either Spyros Capralos, President of the Hellenic Olympic Committee, or Isidoros Kouvelos, President of the International Olympic Academy, are likely to get the nod.

Given the IOC’s rightful emphasis on gender equality in recent times, I would expect several women among the newcomers; someone who looks well-placed is Mexico’s Jimena Saldaña, general secretary of the Pan American Sports Organization.

If Bokel does not make the switch, like Fredericks, from Athletes’ Commission chair to individual IOC member, then I would expect a German to be on the list of newcomers.

New FIFA President Gianni Infantino is presumably now on the long list; I would not be surprised, however, if he has to wait a year or two before joining the group of illustrious Swiss sports administrators who have also served as IOC members.

Perhaps in Lima?