Contact doublets, two bits of glass with the same curves but opposite, can either be left uncemented or cemented.
Zeiss found that with some of their lenses, if the doublets were pushed together, they wouldn't come apart.
The curves were so well made that they did not need cementing.
So they centred the lens elements well and just pushed them together and they stuck to each other.
I don't know how the transmission is affected by this arrangement or how accurate curves need to be to stick together, but glass can do this.
I suppose with extremes of heat or cold they might separate or maybe crack, but the lenses made like this worked well.
I think that these lenses were uncoated, but am not sure.
I don't know if coated elements would stick together if the curves were really accurate.