In Barcelona I asked why it was called the 4.2 and not the 4 and was told it relates to the generation of HMD devices which it is in. For example, 2019 is the third year of HMD devices so these phones have the .2 suffix; the 2017 was the devices without a .x suffix, 2018 had devices with .1, etc. ...
Except that this doesn't make sense. There were several devices launched in the "2nd generation" without .1 on the end of their name, and in Barcelona there was also the 9 (not 9.2) and the 1 plus (not 1.2 plus, but sometimes written as 1.1 plus! - even in HMD's own presentation pictures - check the livestream recording).
Why am I explaining this? Because I just want to point out (again) that HMD's naming scheme doesn't make sense in any logical way. It might make sense in a marketing way, and I'll have to assume that it does otherwise I really will go mad.
So the answer is that nothing happened to the 4 and 4.1, they never existed.
The only other explanation I can think of for the choice of name 4.2 is as homage to the Hitchhiker's Guide to the Galaxy's ultimate answer of 42
So, "don't panic", the name makes sense