[hattend]

The Klingons got smoothe heads for TOS from Kingon doctors trying to create “augments” [Augmented Klingons] from human augment DNA - ST Enterprise, season 3 or 4

They got bumpy heads again because they cured the “augments” virus [alluded to at the end of the augment arc in ST Enterprise]

Real reason was TOS had a crappy budget and couldn’t afford the prosthetic foreheads.

[tanknetter]

Real reason was TOS had a crappy budget and couldn’t afford the prosthetic foreheads.

I really liked how they dealt with the incongruity in the DS9 episode "Trial and Tribbleations".

No one from the uptime DS9 crew could figure out that the smooth forehead Klingons were really Klingons. When they (I think it was Chief O'Brien) asked Worf about it his response was a typically curt "It is something we don't discuss with outsiders".

I think they should have just left it at that, rather than trying to deal with it retroactively in Enterprise.