は・
"I can't speak for A, but B …": you put one case aside as a different matter, without judging it, and say something firm about the one that counts.
A holiday might be another matter, but we can't close the shop for three whole hours in the middle of a weekday.
A hundred years ago may have been another matter, but for a company today to rely on paper records alone is dangerous.
How to form it
Noun + は／なら + いざしらず
は is "as for", なら is "if it were". With a time or a kind of person either is common: 昔は／昔ならいざしらず. Also written いざ知らず.
After a clause
Plain form + なら + いざしらず
本人が望んだならいざしらず.
- Before it
- The case put aside: another time (昔), another kind of person (子ども, 素人, 他人), another situation (休日, 緊急時).
- After it
- The case that counts and a firm verdict on it, often a rebuke: わけにはいかない, べきではない, とは.
- Where you'll meet it
- Editorials, essays, speeches, pointed remarks. Mostly one to read: in everyday talk people say ならともかく.
In use
I can't speak for the old days, but now even meetings with people overseas can be held online.
If it were what they wanted themselves, that would be another matter, but the family shouldn't decide their future for them.
An emergency might be another matter, but there is no reason to skip the normal procedure.
いざしらず or まだしも?
A child might be another matter, but for an adult to do a thing like that is shameful.
A child is a different case, put aside without being judged. The point is the adult.
From a child I could put up with it, but for an adult to do a thing like that is shameful.
From a child it wouldn't be good either, only easier to put up with. From an adult it goes too far.
まだしも needs a worse case to follow. いざしらず doesn't: 昔はいざしらず、今では… only says that times have changed.
Close neighbours
は・ならまだしもN1
The first case isn't good either, only easier to put up with; the second goes too far. Common in conversation.
Being late once I could put up with, but being late every week is a problem.
ならともかくN2
"It would be one thing if …": names a case you could accept. What follows is usually an objection to the real one.
From a child it would be one thing, but an adult making that kind of excuse is a problem.
Check yourself
1What is the writer's point?
昔は
Choose an answer to see why.
2Which one fits?
他社
Choose an answer to see why.
More detail
Word for word it is "I wouldn't know about …". Whether you really don't know is beside the point.
More sentences
An organization of ten or so might be another matter, but one person cannot possibly manage this company of a thousand employees.
Being two or three minutes late might be another matter, but keeping someone waiting an hour without a word is rude.