My understanding of this, as an RCAF junior officer, is that when wearing NO 1A order of dress (ceremonial, medals only), which is what I was directed to wear for attending a 11 Nov ceremony, I do not have the option to wear Oxford shoes, and as a consequence, I shall wear my ankle boots with my 1A DEU. I believe Oxford are appropriate for all NO 3 Service Dress, at the office and for general business.
What do think of that? Would you say that if not told otherwise, wearing ankle boots with 1A order of dress is in accordance with the dress instructions? I witnessed many (if not all) senior officers wearing 1A with Oxford shoes during ceremonies, so I guess there is a permanent instruction coming from COs allowing that mix.