Well, you can do that...
So just use lab x on Mondays shot and lab y on THursdays shot? OR just mix them both together in a 20ml vial....
And it wouldn't hurt anything, but I agree with what was posted about running one brand until you've used it all then switch to the next brand.
That way if you're responding to one better than the other you will know exactly which one it is.
So, a cycle would look like this:
Lab X Mon/Thurs until all gone
Lab Y Mon/Thurs until cycle complete
Do not mix them together in the same vial if you want to be able to tell if you respond to one better than the other.
-UNLESS-
If you don't care about knowing which one may affect you best, or maybe you have already run them both separately before and both worked the same for you, then, yes, you can mix them in the same syringe or vial if you wanted and it would not cause any problems.
I would highly recommend that you go with what I've outlined first, though.