Before doing research in old records, it is a good idea to become familiar with all the variants in letter formation. Many errors are made by people who are not familiar with the handwriting styles of the colonial and pioneer periods in our country. Since I can't give you samples of old handwriting via email, I would like to recommend that you get a book on the subject and study it. Both the capital and lower case versions of these two letters look the same in the handwriting of some of our ancestors.
Vowels are often hard to distinguish too.
When looking for a name, let's say, in the census, if you can't find it, try exchanging the vowel for every other vowel. One of my ancestral names is Chilson. I have found it as Chalson, Chelson, Chilsen, etc. Another of my ancestors was named Relief, nickname Leafa. Thus, the name Melissa may look like Melifsa and, therefore, be misinterpeted.