This is unimportant difference. CRC handbook shows pKa for two isomers of C4 acids as 4.83 and 4.84, for C5 acids as 4.77 to 5.03, for C6 4.84 and 4.85 (incomplete set) for C8 - from 4.6 to 4.9.
Acidity constants are measured in water solution. Higher acids interact with water in different manner and measurement show greater error.