How are "Visited Airports" computed?

Someone asked me recently about how I count "visits" when computing visited airports. Specifically, the # of visits shown in the list of visited airports often doesn't match the number of flights in which that airport was recorded.

The issue arises from my definition of "visiting" an airport. Of course, this has no formal definition, but for me it's decidedly focused around arrival at an airport. After all, "let's go visit Grandma" is about going to Grandma's house, not leaving it. (Besides, it's almost always more of an achievement IMO to land at an airport than to takeoff from it.) So I'm really (mostly) trying to determine arrivals.  In that vein, if you don't log any landings, then the airports won't show up as "visited".

My heuristic (in addition to below) is this:

1. If a flight has a single airport listed, I count that as a visit.
2. If a flight has multiple airports, then I ignore the first airport in the list...
3. ...BUT if the first airport in the list above has no previously recorded visits, then I do count it as a visit.

The idea is that if you fly down to Martha's Vineyard for the weekend, going (say) LWM->MVY on Friday and MVY->LWM on Sunday, that was only one visit to MVY. Ignoring the leading "MVY" on the Monday flight achieves that. If on the intervening Saturday, you did some touch-and-go's at MVY (recording either "MVY" or "MVY-MVY") then you'd get two visits: LWM-MVY and MVY (or MVY-MVY). The Sunday departure (MVY-LWM) is just the completion of the visit, not a new one, so ignoring the MVY has the right result.

The logic above also prevents "MVY-MVY" from registering as 2 visits. After all, if you don't leave the pattern, it's really just one airport, right?

The reason for (c) above is to handle edge cases where you might miss an airport altogether. E.g., if you fly commercial to an airport to pick up your airplane from an airport that you've otherwise never been to (e.g., a few years ago I flew SouthWest Airlines to Sacramento to pick up our club's Mooney at Stockton; I've never otherwise been to Stockton), it should register at least one visit.
Again, there is of course no "official" definition of visited airports; it's just something I thought would be fun, but above explains why the math might seem a bit strange.