You mean
Current LC has been approved, use Unused approved substitution labour with matching profile then PD of current LC can be used for substittuion
Aliens original PD can be used with Labor Substitution if
1) LC has been certified but I-140 has not been filed/rejected for any reason.
2) I-140 has been withdrawn
In this case you will submit proof of original LC PD when you file I-140 with Substitute LC.
SECONDLY,
In some cases (if you have a great Attorney like Rajiv !) Original PD can be used even if someone has already used that LC( For example, it ways AAA's LC, he left the company, BBB used his LC to as SUB.. Now AAA wants to use PD). Here you have to prove the HARDSHIP or similar for not using the LC & using PD. .. this has limited chances of approval.
For those who feel that we are deviating the thread
GP is more knwoledgeble and my questions will make everybody better understanding for how and if condition for substitution labors which most of us will be pondering if we get one