Steps to be followed in order to migrate the code
TDLByte #11
Step 3
Load Default TDL code of Target Release
Target Release: Tally.ERP 9 Release to which the customization has to be migrated to. For example let us consider Release 5.0 as target release.
  Go to Tools Preferences Compiler/Execution Options
  Uncheck the highlighted option as shown below. This loads the Default TDL of the Release
to which Tally.Developer 9 belongs to i.e. Release 5.0.
Should I generate compatibility Metadata for Release 5.0 too?

If the Target Release was lower than Release 5.0, then Compatibility Metadata should be generated. But, from Release 5.0 onwards the tdlserver.ddif file is available by default.

So now we have tdlserver.ddif file for the base release as well as the Target release.