I recently purchased what was left of a warehouse full of ICF blocks from a distributor who wanted out of the business.   I have a huge oversupply of corners as a result.   Unable to trade them or sell them I'm thinking of cannibalizing the corners.   2 feet of each corner constitutes a perfectly good straight ICF block with plastic spacers and all.    Cut the 2 feet off of each corner and you have 2 foot straight blocks.  Normally straight blocks come in 4 foot lengths.    My question is are there any known stability issues with using 1/2 sized = 2 feet blocks or will that be perfectly fine?   

Another issue is mixing different manufacturer's blocks.   If I make one wall of a house out of brand A blocks and the rest of the house out of brand B blocks will there be stability issues?   I plan to stop the wall in two specific locations.    At those two locations there will be no interlaced overlap.    Are there known stability issues with using different manufacturer's blocks or will that be perfectly fine?

You should have no problem using 2 different manufacturer's blocks. Using two foot long blocks will only present a problem if the cross tie is too far from the end of the block. You could get some bulging a it's a potential blow out point. Glue it or bridge it with some plywood. Lining up the vertical studs can also be a pain in the neck, but if you don't do it right, the sheet rockers will hate you. It's also going to take forever. Good luck.

How about using the corner blocks for all the short pieces you need up against doorways and windows?

I went to see a house being poured that my ICF supplier was building just before I built my house. He used Buildblock for most of it, the block he had begun to distribute, but had one wall or the garage, I don't recall exactly, built of Logix blocks, which was the line he was dropping.

Jacktca, we use our 8' block all the way down to one web or 8" pieces.

I wouldn't expect any problem from any 2 ft piece if it came from a block you are comfortable with. You may need to pay attention to width (depending on your finish out). E.g. Most blocks are 11 inches wide, mine is 11 1/4 inches wide etc. Also, block height might matter depending on how you plan to mix things up. Mine is 18", most are 16", some are 12" one that i know of is 16 3/4". Regards

I have a huge oversupply of corners as a result.

Add a bunch of bump-outs to your build.

A breakfast nook for the kitchen.
A daybed in a hallway.
A reading nook for the kids.
A solarium for the laundry room.
A workbench in the garage.

Bumpouts can use up corners pretty quick and help strengthen long straight walls.

Very good point Texas.   I looked at the online specs earlier and the fit was just peachy.  Brand A is 9" wide and brand B is 9" wide according to the specs.   I checked with a measuring tape.  In reality brand A is 9" wide but brand B is 8 3/4" wide.    As for height I'm not worried because the top row is going to have to be cut anyway.