I think 'lemon' cuckoo is a desceptive term. Citron/Zitron does translate to lemon in some European languages. And very often when the name lemon or citron is used it is referring to the cream gene, ig. As you mention, in the cream light brown dutch bantams or the lemon mille fleur the gene is cream. However in lemon blues it is not cream but is apparently simply gold birchen with blue.
I used cream quite a bit back in UK. Its effects can be variable, on gold ranging from cream to just about silver. Such as on the cream light brown dutch (I did that colour with leghorns). It does not give that pinkish effect, as in the lemon mille fleur, unless it is with mahogany.
From what I have seen of lemon cuckoo pekin bantams back home in UK, they are buff birds with barring & reference to lemon is another of these desceptive names sometimes used.
I don't know whether they used the name in US but for a while blue laced silver wyandottes were referred to as lilac laced in UK.