Congrats to you for jumping into Lenormand, Phoenix! I’ve looked into it several times, but like Oracle I just haven’t made the click with a deck yet. I’m still on the hunt!
I’ve never dealt with an incomplete spread before- but I don’t think it should stop you from keeping in mind the messages that came across in the cards that you did see.
That being said, I wouldn’t try to piece out the “whole picture” and overall message using an incomplete spread- it seems to me like (a significantly less extreme) case of skydiving without checking all of the straps and buckles or driving a car for the first time without having read the whole manual- the missing pieces of information could be the most important.
I’m afraid I don’t know enough about lenormand to offer specific advice about using that deck, but when it comes to cross-checking with multiple methods of divination, I’m in the school of thought that you can double up any methods of divination- they each have their own strengths and weaknesses, so there’s a lot of benefit in using/cross-checking across methods 
All in all, I’d say it’s a good idea to back up/cross-check your incomplete reading with a full and complete spread in another method! 
Good luck and blessed be, Phoenix! 