[Jackarutu]

A thought occurred to me that due to the fact you have stated that these three springs you are dealing with came from an individual rather than an Airsoft retailer have you considered that the spring you found in the Modify package is not the one that originally came in that package?

How about perhaps the spring that came loose with no id and actually tests in the proper range for a Modify S90+ is actually the one that should have been in the package but the person you bought them from got them all mixed up?

As you mentioned and others here also mentioned a Modify S90 + would have a band of tight coils on one end and if the spring you found in the Modify package doesn’t have those I doubt that it is a Modify S90 + spring.

As I say just some thoughts I have, no way to prove this but it could go a long way to explain what you report here on these posts.