Often when we send manuscripts, we get an auto-generated response saying that 'if we don't get back to you, please consider this a regretful no'. I accept that.
In May last year, I approached a good publisher with my manuscript. In July, I received a response saying that my work had 'substantial potential' and they 'might be interested in making an offer for publication', but were pressed for time, so please contact them in November or December. I did so, but have had no communication at all from them thereafter. I sent a reminder last month, which also went unanswered. Is this normal? How long does it make sense to keep my hopes up?
How wonderful to have received such a promising first response - well done!
I think I would call them so as to be able to actually speak to someone, repeating what you've said above. Good luck.