Excel Formula: How to increment-alphanumeric-column-by-1 Part 2

This is a follow up to previous question posted:
https://www.experts-exchange.com/questions/28960037/Excel-Formula-How-to-increment-alphanumeric-column-by-1.html?anchor=a41732303&anchorAnswerId=41732303#a41732303

Received a valid, correct answer to that post (thank you Ryan).  I would like to go ahead an inquire and expand on the previous question posted.

My SKU pattern is MPSK-00001-001.  The prefix of the pattern is constant "MPSK". The dashes are part of the pattern and must be retained. And finally must retain leading zeros, padding zeros.

Would like to auto increment the middle part of the pattern the "00001" portion of the pattern +1 when column D(vendor) has a value.  From a previous post I applied the formula =IF(D2="","", "MPSK-" & TEXT(COUNTA($D$2:D2),"00000")&"-001") and this produced desired results to generate the main SKU base.
 
-ELSE-

When column D (vendor)  is blank increment the SKU suffix portion of the pattern +1.  How to nest IF, or how to accomplish the else portion of this question?

The datasheet that I have in Excel I can not add more columns.  So I need to apply the formula starting from column N, and carry it forward to however far I need to drag it down in the future as the list grows.  

Screen shot items in column N(variant SKU) black color were populated with the formula of =IF(D2="","", "MPSK-" & TEXT(COUNTA($D$2:D2),"00000")&"-001") , items in green are the desired additional output.  How to extend the previous code formula is the follow up question.