Lighting, Light Fixtures, Ceiling and Exhaust Fans - Installing round light plates on rectangle box

I am building a home in the Bahamas and found my electrician roughed in all my designated light locations with 4" x 4" "smurf" plastic boxes with 2" x 4" rectangular mud collars normally used for switches/outlets. The plasterer then set them flush in stucco.

I wish to order my lights and not surprisingly they have round bases and usually do not indicate the base size. The electrician said there is no problem because all round bases cover the 2" x 4" mud collar.

This is the Bahamas and when I hear "no problem" it usually means otherwise. Is he correct? Given the number of lights I am ordering this will be very problematic if round bases do not cover the rectangle box. My gut tells me they make octagonal boxes for a very good reason.

The base on the light will probably attach to a spanner, which will fit across the two screws opposite each other and the base will cover the extension ring, but I don't understand why they wouldn't have done it right from the beginning, knowing there was to be lighting in the boxes. I know it's the Bahamas, but will there be an inspection? If not, are there even inspectors?

I asked the same question. The reply was the electrician couldn't find octagon boxes with plaster rings! As for the electrical code/inspection...the applicable code is apparently the Canadian code. This is the only licensed electrician on the island. I have been building this house for 5 years now and have had 2 inspection visits. One by the building inspector that came two weeks prior to dove hunting season and hints that 2 cases of shotgun shells would be appreciated. I quickly picked up on the inference and complied and have never seen him since.
The other was from the electrical inspector that told me pool bonding (equipotential bonding) was the same as grounding and that I needed to put 2 grounding rods in the sea! No joke!
(I bonded my own pool, put two dummy rods out and voila!)
So...hear I am tapping the minds of the real world so to speak!

I did confirm that there are no plaster rings for smurf octagonal boxes sold anywhere in Bahamas...they sell the boxes but no rings. It seems it is my fault for insisting on smurf because I chose to build right on the ocean and I have seen metal boxes disintegrate is five years or less.
Tons of smurf (Carlon) available in US, but electrician has no internet and no credit card to purchase...and his phone is blocked by phone company from making international calls so he couldn't call me. LOL
Immigration won't let me bring in US electrician because we have one on the island...his cousin!
Watch for my book release on building in the Bahamas under comedy or horror fiction!
Is there a stardard round base size for lighting? I need 4.5" corner to corner even if the spanner works. Even the manufacture websites I wish to purchase from omit this dimension and simply say standard size base.
Google was no help either.