Just in case you don’t know, celluloid is an early plastic. It was produced from the 30s through the early 60s, though less so in later years. It was used to make some very lovely ornaments and plastic figurines.
It is also quite fragile and often pieces with damage are found. Especially the celluloid reindeer are prone to having a missing antler or two. Sellers often confuse celluloid with the later “hard plastic”, which was produced in an overlapping time period. Without being able to examine the piece, guidebooks are your best resource in determining whether a claim to be celluloid is likely true or not.