Steps from patio lay on old mortar bed?

[pablo-paul]

Hi all I'm creating some steps from the patio upto some doors. I've lifted the slabs which were laid on a full mortar bed. The adhesion was pretty good but other than a couple of small areas the old mortar bed is still in place on top of the sub-base. Question is is it ok to lay the first course on this as it's a really nice surface? Or should I break it up and go back to the sub-base.
I've done kitchens and bathrooms but nothing else like this before so I'm sure I may have missed something.