A point to bear in mind is that "holding pools" are tidal in nature. By that I mean, most airlines are highly seasonal in their training programmes. Airline pilots are very demanding on training resources. Established pilots usually tie up around 8 hours of simulator time each (16 hours per rostered pair) per annum. Add recurrent ground training, line checks, and command training to the mix, and it comes to a sizeable training commitment.
New induction training, places a heavy burden on the available training tracks. For cadets this is especially so. This is why such training is concentrated in the airlines low season, usually the period November to April, although there is often overspill.
This means that placement opportunities tend to be programmed in the Winter and Spring, with significantly lower demand at other times of the year. It follows that an intermediate training course ending in the Autumn, is going to be much better placed (all other things being equal,) than one finishing in Winter Spring or Summer, when the resultant wait time may well be longer.
I am aware of placements being offered to graduates who have completed their courses this year, so a "hold pool of 18-24 months" seems highly unlikely. However given the tidal nature of recruitment and the commercial demands of the airline customers, such things should never be dismissed. In the past few years there have been waiting times for placements of anything between zero and over 12 months.