Two different first names, same person

[NextMove]

My Italian Mum used a mixture of her first name and shortened first name for a variety of documents in Italy and the UK. The shortened version appears on her birth certificate and long version on my birth certificate. How do I prove they are both the same person?

The comune has suggested starting with her baptism certificate, so Im sending for that today. What else can I do please?

[Italysearcher]

The name used on her official Italian birth record is the legal name. The baptism record may add even more names!
What about her marriage certificate? What about other UK documents?

[NextMove]

The comune have asked me do send for the baptism certificate so I must do it, whether it adds names or not.

Shortened name

Birth certificate
Residence certificate
Italian passport
Letters from ANED re war pension
Document from Ministero del Tesoro

Long name

Marriage certificate
Questura document
My birth certificate

Im sure there are more that could be added to both lists.