Can we say now that

“If that make[s] it a true statement, then it’s a likely candidate for the subjunctive mood.” (omitting [s])

is wrong. While

“If that should make it a true statement” or “Should that make it a true statement”.

is correct?

Or can we consider both to be correct?

“If that make[s] it a true statement, then it’s a likely candidate for the subjunctive mood.”

This statement is a condition of uncertainty meaning, in very formal English, it should state, “if that make it a true statement” instead of “makes”. You may ask why? Because “makes” is indicative, but you are not indicating anything; you are stating an uncertain condition. Here’s a way to rewrite it out of subjunctive:

“If that should make it a true statement” or “Should that make it a true statement”.

Sigh, the death of the subjunctive can even be found on forums that are meant to try to save it. Nevertheless, if you all be very didactic and do your homework, you shall see the errors for yourself.

But the sentence with “were” instead of “was” still has two serious problems that any good copy-editor would catch:

1. The phrase “instead of” can be read as comparing “on a tropical island” with “at my desk working” — so the second alternative becomes “vacationing at my desk working,” and

2. The need for parallel structure requires that “at my desk working” have a verb like “vacationing,” e.g., “I wish I were vacationing on a tropical island instead of being at my desk working.”

The smoothest rewrite of the sentence, addressing both problems gracefully, is probably this:

“I wish I were vacationing on a tropical island instead of working at my desk.”

My copy of The New St. Martin’s Handbook says both ways of stating the past subjunctive can be correct, depending on the situation.

“Because the subjunctive can create a rather formal tone, many people today tend to substitute the indicative in informal conversation.

If I was a better typist, I would type my own papers.

Nevertheless, formal writing still requires the use of the subjunctive in the following kinds of subjective clauses: (clauses expressing a wish and clauses expressing a condition that does not exist).”

Perhaps because I write genre fiction, this loose tone sometimes feels like a better fit.

Come to think of it, there is an error in that song that bothers me every time I hear it. It occurs in these lines:

If a tinker were my trade
Would you still find me
Carrying the pots I’d made
Following behind me

A tinker is actually one who repairs pots, not someone who makes them. I used to live next door to a tinker’s shop in a back alley in Esfahan, Iran. His job was to reseal the bottom of pots after holes had worn through after many hours on the fire.