I'm running into the same problem. There just aren't enough validated vowels. How else can we "count" through the glyphs, in a SIMPLE way. Chelsea said "I'm not mathematical," so I think we can safely, for now anyway as we try to prove this theory wrong, discount things like prime numbers, multiplication and division (which therefore excludes averages). I think it's unlikely that we have to SUPPLY additional letters, unless the system is simple.

Taking account some previous work that's been done here, Chelsea's reference to birds might be to cuckoo clocks (point to the "12" or "N" position), or, as someone else pointed out, to cardinal numbers. Now cardinal numbers don't help (cardinal vs. ordinal), but cardinal POINTS do, as they refer to the true directions of S, E, W, and, of course, North. When you see a clock for the first time, you're tempted to start counting from 12. Maybe that's what we should be doing....

Some thoughts...