Jeff L Headley said:
Were the through tennons ends beveled first and then the bevel trimmed flat afterwards?
Quite probably. Those I have seen were trimmed level with the block, so why not bevel the tenons first if it eases them through initially?
I have seen very few North American side- and dining chairs, but those I have seen had seat rails which were through-tenoned and wedged (at the back only).
Also, many bookcase/linencupboard doors frames were through-tenoned and wedged.