Absence of the Symbol Resembling '4' in the Very First Folio 1r

[Dobri]

Since the numerals 4, 5, and 7 began to take the forms we are familiar with today by the end of the fifteenth century, 
what was the possible inspiration in the early 15th century for the inclusion of the symbol q in the cipher manuscript?

Was there a limited use of q in parts of Europe in the early 15th century?

It appears that qo can be found as early as 1339 in the arithmetic manuscript Trattato dell'abbaco written by You are not allowed to view links. Register or Login to view. (c. 1282 – c. 1374).

Notice also the use of the numeral 5 depicted as more 5-like than 4-like.