Any Vanda with flowers this big, full and flat has V. sanderiana ancestry, virtually every single one of them, whether you think you can see it in other ways or not. It seems to be a fairly typical V. Rothschildiana to me and it clearly isn't pure V. coerulea, but there are many other hybrids of similar appearance. Remember also that V. Rothschildiana has had generations of selective breeding within the hybrid over the years, and re-makes with highly selected forms of the species, many of which vary greatly from a typical first generation hybrid.
If it was my plant I would not doubt the identification. It seems to be nice form of that hybrid, and obviously very well grown.
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