The Yiddish origin of
schlock is a red herring (as opposed to a schmaltz herring), since the word is widely used nowadays by people who are neither Jewish nor speakers of Yiddish. This is why it can be found in most English dictionaries. The question to be decided is whether the word is widely enough known around the English-speaking world to be treated as common and, specifically, whether its use is mainly confined to North America.
As with
schlep, that was
discussed a few years ago, there is quite a bit of usage of the word in Britain, Australia, etc. The News on the Web (NOW) Corpus has 106 examples from Great Britain, from a range of periodicals:
Guardian,
Telegraph,
Independent,
Daily Mail and, yes, the
Jewish Chronicle. In terms of frequency, Britain, at 0.25 instances per million words, was more than half the frequency of the US, at 0.43. Australia, Canada and Ireland used the word a bit less frequently than Britain. It's noteworthy that none of these quotes felt it was necessary to explain the meaning of the term.
The NOW Corpus only goes back to 2010, but the word
schlock has been in some use in Britain well before that. The earliest quote from a British writer I found (via the OED) was from Len Deighton's
Billion-Dollar Brain (1966):
The schlock-shops were afire with sale signs and smiling suckers.
In 1968 Kenneth Allsop wrote in
Punch of:
...the accumulated realisation that the New World's promise, that of a fresh beginning on virgin soil, beyond contamination from the stinking bone-pile of Europe, was illusory. Utopia was a schlock joint, after all.
In 1972 Clive James wrote in the
Times Literary Supplement:
As the critics had had no trouble proving - since anybody who could count without taking his hands out of his pockets agreed with them - Love Story had made all its money by a trick, the trick being to dress up a piece of half-witted schlock romance as a hip tragedy.
These days the word seems to be used more often than not, as in the Clive James quote, for products of the entertainment industry. Could it be classed as, to some extent, a piece of show biz jargon, unfamiliar to many of those who don't read film and TV reviews? Perhaps, but I'm not convinced.
Of course I have to take serious note of the fact that two forumites had never heard of the word before, but even so, I'm not persuaded
schlock should be changed to rare, so I'm leaving it as it is for now.