@wing044 - thanks for pointing these out. The main problem is that actual data is missing for many locos, so data has been estimated, usually to the nearest 5kmh (e.g. 155kmh). Others have been converted from mph presumably, hence 153kmh.
I think there does need to be some tweaking of top speeds, especially in the steam era, as the top speeds in the dat file do correspond to approximate "top speeds" of the loco, but not the top speed usually allowed in practice. This means when diesels appear, there may even be a drop in speeds, which isn;t actually what happened, as diesels generally operated at higher average speeds...