Someone correct me if Im wrong but I think you bid for a CD line using the double slash //

Here the deal though anything after the double slash is read by a human first before the lines are awarded. So if you bid for a CD line and can hold it, you are awarded the CD line before you will be awarded a normal line.

So here are some examples

Pilot seniority 1 who can hold a normal line or CD line Bids
D1-3 DSA DSU p4dt Nop5dt//CD 01 02
This pilot would be awarded the CD line 01

Pilot Seniority 500 who sometimes holds a normal line but this month doesn't quite make it bids
D1-3 DSA DSU P4dt NoP5dt
This month this pilot is awarded a reserve line because he failed to bid for CD 02

Pilot seniority 1500 who holds a reserve line but bids CDs just in case
D1-3 DSA DSU p4dt nop5dt//CD 01 02
This pilot would be awarded CD line 02