Generally I copy the nutritional info off the packaging, but if there isn't any, and the above link doesn't have the product or I just don't have the packaging on me, then I google the nutritional value and include the brand. That often works. Another thing I have done is contact the firm - i.e. BP now sells a large range of food in their Service Centres. I e-mailed them and told them what I wanted and got more than I required at that time, but it has proven to be a godsend for me. In an attachment they sent me their range of hot and cold foods, including cakes/biscuits/slices, with the entire main breakdown, except fibre :-)
I manually enter those and have them on my favourites. I refuse to use other member's nutritional info entries, and I suggest you be VERY careful about adding any SP Member's info - I have browsed through a lot of found many errors, and/or omissions - i.e. no fats/protein/fibre/sodium showing and sometimes the calories are way out. I have had the packaging with me when checking it.
If you continue having a problem, find info, you can message me if you like!