In reply to Lasse Makkonen.

Thank you, Lasse Makkonen!
IIUC, your argument is quite strong to use `type=6` i.e., SAS: `QNTLDEF=4` which you also attribute to Weibull(1939) .. which is interesting in itself.

I'm about to update R's help page `help(quantile)` (or `?quantile`).