As a very basic principle, yes. But note that a LEF file is simply a textual description of your license entitlements.
- If your LEF has a line with TIMELIMIT, for example, the product should stop working after the date specified in that line.
- A LEF can also become obsolete even when the product is during maintenance in which case contacting Qlik Support will provide the correct and updated LEF file.
- If PRODUCTLEVEL is there and it has a date, your product will keep working as long as the version run has been issued prior to the date specified, for example, if the date is "2018-12-31" that license cannot be used in a QlikView April 2020, since this version was released after December 2018. Reverting to an older version, released before that date will work fine.
I suggest you contact either Qlik Support, if you have a current maintenance agreement, or with your Qlik Partner or Qlik Sales team to see what could be causing that issue.