Do you need to continue to pay LTD premiums if on LTD to maintain tax free status?

I am currently on short term disability and will be changing to long term disability at the end of January 2020.  At that point, my employment will end and my income will be coming from LTD and SSDI (also starting January 2020).  I have been paying the LTD premiums (post-tax) for 5 years so I know that due to the 3 year look back rule, any distributions coming from LTD will be tax free (where as SSDI is taxable).  My question is this:  If you have been paying your LTD premiums instead of your employer, once you are on LTD do you still need to some how pay the premiums to maintain that 3 year look back rule so that the distributions stay tax free?  Or do you just stop paying the premiums once you are on LTD?  I tried calling the IRS and unbelievably the person I talked to could not answer the question and had no clue who to send my question to.  She told me to look at the IRS website, which I had already done many times before.  Thanks for the help.