Hello everyone

I'm a beginner, starting out with De Silva's Primer. I'm a bit
confused about her pronunciation guide; specifically, she has the
following:
t is pronounced like th in thumb
d " " " th in they

When I compare this to Narada's Elementary Course, he doesn't have
these two letters, only the forms with a dot underneath them.

Do these two letters actually exist, or is it a typo on someone's
part? How is a word like 'putta' pronounced, for example?

Thanks for any help.

Swishsticks.

Ps : I really appreciate this group - great work!