This was a fascinating nugget of useless information, thanks for mentioning .

As its tangentially relevant, I would mention that AA often has the same flight number, same calendar day - just different destinations, e.g. I took the AA2440 from MIA-SKB and then back again on SKB-MIA. It turns out that is as AA is running out of flight numbers with only 1-9999 so their systems are designed for it. Clearly BA aren't that close. As with AA it is operated by the same plane I guess it doesn't matter about a callsign (how do I even see that?).