Wonderful, Anne. I'm going to try and solve this one by research (I'm recently resident in Belgium and reresearching my website accordingly)
Here are my 'working thoughts' (credit to all contributors), which I will also share with my Belgian professional contacts via email.
I really hope that we can solve the puzzle, although I guess I'm not the first to try.

Van Haeleweyck Frères was founded in 1855 and were still in existence in 1929. Their address was 63-69 Rue du Vautour (Gierstraat), Brussels. the company registry number, 3646. Clearly the company was selling in bulk since the receipt lists 54 each of 3 different product lines" The front of the building is marked "Lusterie - Van Haelesweyck Frs - Pendules" and the invoice adds 'Verrerie d'eclairage' (Lighting Glass)- Oréor
It seems clear that these designs were intended (mainly) for use as table lamp bases. (The last one was not the first found with it's original lamp fitting)
I think it's clear that the word 'Oréor' is NOT a factory, but must then be either a designer or a brand name. (This is also indicated by the format of the
Van Haeleweyck paper ; that they were exclusive distributors). Implies that they may have ordered or made designs (moulds) and then will have had the items produced by a third party (outside Brussels). The fact that they were sometimes described as 'French' may be misleading us?!
There are a few added clues for deductive reasoning:
Normally the Oreor supplier would be within 'easy reach' of Brussels, if that IS indeed where they were distributed.
(This implies more likely candidates Scailmont?, Sars?, Hunebelle? Muller Freres?)
All the designs seem to be from the same designer. (combining geometry and round forms)
Considering there are several different designs, all clearly marked, there are not very many survivors, implying that production numbers were low. (It was not identified at all by Hartmann or Kappa, and GlassMessages have only found a few!)
The "oreor' mark is into the side of the mould (not the base!) and written in script. This is quite unusual as a style of marking. Scailmont is one of the few factories that did it this way, and indeed even the handwriting is quite close to that on Scailmont/ Heemskerk/ Catteau items. also Carillo?
There is usually a special significance to chosing a trade name. 'Or-é-Or ' could be a reference to gold, but doesn't seem that likely. Could it be an anagram, regional name, wife's name, initials, or a pun?
Production quality is 'mid-range' and there are signs of flecking on the satine surfaces. The Items are quite thickly cast, although there are no traces of seams around the body (as far as I've inspected)
So far there are 6 models found, and they were probably available in white, light amber (honey), light-blue, sea-green, uranium?green and light purple.