You have left off the 7.3 million options that GBA have in MMR, this bumps up GBA's share by 2.5 - 3%. Advent also owe GBA $500K in loans.
GBA's share of PEP11 is closer to 13% and compared to BUY is trading around 20 times cheaper given the low number of shares on issue.
Apart from this your analysis is fine.
DYOR