Yes, it’s both unlikely the lead actually varies by that much in practice (it’s made of wire and wire is very uniform as a rule) and also unlikely you’d get a worst possible case part and a worst case via hole at the same time. You don’t know what the distribution of the parts within the tolerance, but there’s a very small chance either will be at or near the limits - theoretically 0% that either part will be right on the edge, and square that for both at once. This is the basis of the RMS error accumulation logic in IPC 7351B as described here: Capacitor 1206 footprint: correct for the parts I will be using? - #10 by johnbeard
How you want to handle that probability is up to you and that’s why between IPC’s various documents and Wuerth themselves there are at least 4 different options, even if you limit your concern only to lead tolerance and hole diameter tolerance.
Pitch tolerance is most likely negligible in practice here because the leads are flexible enough to conform to the hole centres anyway. In fact the pitch isn’t specified clearly here, as the dimension is between leads 1 and 3. So it’s not clear what a single pitch may vary by. Many parts have a separate tolerance for the pitch as it’s usually better controlled than the general tolerance, but it’s not so specified here, and neither is the perpendicularity of the lead - ISO 2768 m’s 1%, maybe?
There’s also layer registration tolerances and the drilling position tolerance on top!
It’s an eternal library problem whether we listen to datasheets or apply some common standard (and if so, which one to listen to). Generally to this point, we have made do with:
- DS is usually OK unless they really seem to have been drafted while on crack
- Bigger than IPC 2222 minimums if the DS doesn’t say (or looks particularly bogus)
- IPC 2222 maximums provide a clue for how big the “sensible” window is, but doesn’t say whether you should actually target within the min-max window
And mostly the world hasn’t ended yet!
IPC 7352 is the “new hotness”, but the editorial quality of the standard is utterly dire which does make me wonder about how reliable it is technically. Some of the equations are now outright wrong, in my opinion.