no problem at all to add profiles without last-names. Just go into Edit Profile and delete the field. The TWO drawbacks to this that I am aware of, are
1) the "Go To" feature in the Tree view, which indexes by last name, will not list such people.
2) if you later merge with another profile that has some value in this field, that value will automatically be accepted (so you'll need to remove it again). This is only really an issue in lines that get merged OFTEN.
In the Biblical Tree we use the convention of using a period (.) as a "last name". This solves both of the above issues.
pretty much MOST "common-people" did NOT have Family-Names until Napoleon forced the issue to improve taxation. Other countries followed him, in a general west to east direction across Europe.
This was even more so with Jews, with regard to "official" records, as many countries considered us "non-people" who simply were not recorded, let alone have citizenship and rights. My grandmother, born 1922 in Romania, only received her citizenship after WWII.
In Bohemia, the critical date for adoption of surnames was 1788. The 1783 Jewish Bohemia census typically shows patronymic names, whereas the 1793 Bohemia Jewish census generally shows "inherited" surnames. The Familiantenbucher shows the surnames, and if you are lucky also the name that they used before adoption. As the books cover nearly 40 years of family changes (from around 1790 to the 1830s), there can be confusion when listing people who died before the general surname adoption in 1788.