Definitely eggs, I actually witnessed a female lay them on the glass after posting the OP

There are many more batches now (5-6). Pretty hard to remove, I gently scraped several with a dough scraper into a vase with tank water, and added an air stone. They are nearly impossible to see.
The BA Tetras have poked at them a bit but they seem to remain adhered to the tank wall for now.
Which species of cory do you have?
It's important that the eggs and wrigglers, if any hatch, remain in the same tank water as the parents, at the same temp as that tank. I've even rigged a contraption of a small food container with some holes poked into it higher up, sitting inside a cleaned margarine container, to allow easy water changes by changing the water in the outer container, while the eggs and fry are safely inside the smaller one, the holes allowing some water exchange. The airstone sitting in the outer tub.
Use a credit card or even a stanley blade to carefully scrape the eggs off the tank walls, I also prop or hold a large fine fishnet below the eggs, to catch any that fall.
I picked up a breeder box, but I'm concerned that any eggs will fit thru the slits. I'm also concerned that I may damage eggs by trying to remove them from the glass. I'll have to delay a WC (water params permitting) because some of the clusters are quite high on the tank walls. I'll wait a day and see if I can see any development.
Most commercial breeder boxes have holes or slits that are way too big for cory fry I'm afraid! I haven't found any. They're mainly designed for livebearers, who have much larger/more developed fry, not for egg layers. I pinched a tip from elsewhere though. Already had a netted breeder box like this one;
But the netting is still far too large for cory fry. They really are tiny! So I bought an extra large pair of ladies tights, and stretched the leg over the box. Was tricky, but worked perfectly. Suctioned to parent tank, eliminated the need for tiny water changes like in the food containers, and ensures the fry are in the same water parameters from egg to baby fish. Once they're larger, can be transferred to another nursery tank.
My tacky, jerry-rigged emergency fry container;
Freshly hatched bronze cory wrigglers;
Newer improved set up, with ladies tights stretched over the frame of the breeder box
Growing fry in tight netted breeder box
Starting to look like proper cories! Was testing if they'd go for these wafers and which they might prefer. Don't leave too much food in there for long though. A turkey baster is fantastic both for sucking up and moving wrigglers when they're tiny, but also for cleaning out their container.
Same batch, now much bigger and able to live with adults
