Mass emails: When is it necessary?

Some context for this situation.

• I am new to an insurance company, working in their IT department
• I am young, fresh out of college, with 'minimal' experience in a professional workplace. But interned with this particular company twice before I was hired on full-time

We recently have been testing a new version of a software we use for our employees who process claims. I will refer to them as version A and version B.

We had about a 50/50 mix of people using version A and people using version B. When a large number of the people using version B started having problems, I was told to send out an email with the following information:

• Anyone who is currently using version B and is having problems, they should roll back to version A
• If they are on version B and NOT having any problems, then they should continue to work normally.

So I sent that email out to a distribution group we have that would include everyone who this problem could be occurring with, this distribution group included about 100 people who could have had either version A or B. After it was sent, I was told it should have been sent out to only the specific people who were having issues. Since there are about 50 employees who could have been having problems, and we don't know who all was having them, I find it hard to sort through all the employees to find out who was having problems. I was also told that employees tend to follow all instructions sent to them from IT, regardless of what conditions are mentioned in the email. Meaning even if they were not having issues with version B they still rolled back to version A. That was the main reasoning as to why I was told it should have been done differently.

Does this hold true for most professional work places? Was I right or wrong to send out an email that I knew would include all employees that this could pertain to or affect?

Thank you for any advice in advance. I feel like this may be a little opinion based, but i'm looking for an answer from anyone who has experience in this line of work as a professional.