re : minimum sizes of transactions and blocks I see there's a similar question provided here:

What are the minimum sizes for transactions and blocks in Bitcoin?

But the answer provided might be not correct in the light that "A valid transaction requires at least 100 bytes" or am I missing something here ?  See checklist #6.

If relevant to minimal transaction size, my question then would be, was this standard introduced after or before the answer provided.
Also, did the answer provider care about distinguishing between valid transactions and invalid transactions ?
That limit (which is different today) pertains to node policy and transaction standardness. It is important to keep in mind that something that is non-standard is not necessarily invalid. Validity and standardness are two different things, although standardness is a subset of validity.

A transaction smaller than the standardness minimum can still be valid. It will just be considered non-standard and not be accepted by nodes following that particular policy (which is most nodes as that is part of Bitcoin Core). The limit today is 82 bytes which is the smallest size a standard transaction can be.


  If relevant to minimal transaction size, my question then would be, was this standard introduced after or before the answer provided. 


This policy rule was introduced in 2010, long before the referenced question and answer. Furthermore, that wiki page was written containing that information in 2011. Also note that the wiki page is outdated as the rule in question is incorrect.


  Also, did the answer provider care about distinguishing between valid transactions and invalid transactions ? 


The answerer (me) did. The smallest valid transaction is as I state in that answer. Such a transaction will be considered non-standard and will not be relayed per the policy rule, but if a miner were to include such a transaction in a block, it would be accepted by nodes as being completely valid.