En or l' for seasons

Question

This lesson distinguishes between the use of "en" and "l'". It gives examples of both but fails to provide any information about which one is appropriate and when. One of the comments says that they are interchangeable - which makes no sense as the tests insist they are not?

Accepted Answer

Bonjour Brian,
They are interchangeable. See here: en-l'
I hope this is helpful.
Bonne journée !

Answer

They are interchangeable. I can’t recall any example that suggested they weren’t, although the questions may only provide the option of one of the correct answers rather than both for the 3 relevant seasons. 
If you have found one to do otherwise, worth reporting directly though. 
Edit: to clarify, and after some further reading, the interchangeable use discussed here, applies when saying “IN summer/winter/autumn”.
There are other sites that discuss the use of other prepositional constructs and specific modifiers, including “à l’ “, “ dans l’ “, durant, pendant etc
For simplicity, for non-native speakers, some recommend restricting to using ‘en ou au’ to mean “IN (season)”.
https://www.fluentu.com/blog/french/seasons-in-french/
This link is a Canadian site :
http://bdl.oqlf.gouv.qc.ca/bdl/gabarit_bdl.asp?id=3516

Answer

Céline - I think we are talking a bit at crossed purposes.

In the context discussed in the lesson, the ‘en’ and “ l’ “ are interchangeable, but that is not always the case when referring to the seasons, at least as I understand it. For instance, I don’t think you can substitute en for l’ in “ début de l’hiver ...”.

I am not sure if Brian is referring just to questions meaning “in summer etc” or other questions with constructs in which they are not interchangeable.

https://www.druide.com/fr/enquetes/quelle-preposition-porter-cette-saison