Ideally, instead of increasing the number of creatures, a review of the occupied slots should be conducted – many people reserved IDs at one time and didn't upload anything, and it's unlikely they will.
Or simply ignore the occupied/unoccupied slots and, under the banner of a new mod, create a new list of creatures – this will eliminate the problem of occupied but empty slots, and it will be possible to move creatures to other IDs if necessary (if they overlap with someone else).

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Неудачное планирование ведёт к неудаче ...
NCF - мод, добавляющий дополнительных существ в HeroesV 3.1