There are some large gaps in fleet numbers in Lothian fleet anyway.
51-102, 191-200 (both prob reserved for single deckers I assume?), 251-280, 511-550, 595-627, 960-990
I understand keeping 51-99 for single deckers but the others are not being used... some have became available since some of the older fleet has been retired but others have not been used in a very long time if ever.
Going by what I know 51-65 are assigned to the ECB Eclipse Threes I think, even though they display 10051-10065. 101-102 are also ECB 10101-10102 I think, same with 195-199 (10195-10199) unless ECB are now using their extra long fleet numbers as official numbers rather than just adding 10 (singe deck) or 20 (double deck) to their fleet numbers simply to show that they are part of ECB and not LothianCity as they are now calling it. 100 is vacant, along with 108-112, 115 and 124. Numbers 251-277 are presumably reserved for the trams, also 290-300 are not being used (used to be Routemasters who now have their London fleet numbers back). Most of 628-700 are now becoming vacant with Tridents heading out, although 961-1000 haven't been used for a long time, with the exception of the Scanias.
The isolated vacant numbers (200, 216, 390 and 438-440, along with any I've missed out) annoy me, but that's hardly avoidable with a fleet as big as Lothian's.
I also think that there's no harm in filling the huge gaps like 66-100, 511-550, 595-700 and 961-1000 with the new buses, although They might want to wait until the Tridents are gone before filling up 628-700.
I wonder if there's a particular reason why Lothian are going into the 1000s and 1100s with new buses now, rather than sticking to numbers 1-999.