EEA PR, self-employed route, LTD director

[expat2019]

I am a EU national. I came to the UK in 09/2013. I've been self-employed (LTD director) since 10/2013.

I would like to proof that I excercised EU treaty rights from 10/2013 to 10/2018.

As a proof of residence I am going to produce water bills for the period.

Regarding the self employment I am going to produce photo-copies (SAR) of self-assessment tax returns.

The problem is that the financial year does not overlap the calendar year. Therefore there is a half-year gap
between 04/2018 and 10/2018 as my tax returns cover period 04/2013 - 04/2018.

What could be a valid proof of me being self-employed during the gap ?

As a director I paid myself the lowest salary. Therefore I did not pay NIC as I was below the threshold. Might it be an issue?