Baggersup:
Would somebody going sick to avoid striking be silly enough to document their own subterfuge by also claiming strike pay? That's a double paper trail.
A possible rationale is for someone who is genuinely sick to report so to BA, but also give the appearance of striking to BASSA, safe in the knowledge that nobody will have seen them at work.
Were BASSA bright or devious enough to have some stooges who worked during strikes so as to report on who else turned up for work?