I wasn't sure whether to post this as a comment, as it's not a direct answer to the question, but it is relevant(ish)...
Your experience prior to the job is valid (whether freelance or otherwise) and will certainly be considered by prospective employers when assessing your CV.
On the other hand, and making an assumption, if the role you have been employed in is a Graduate Role, then your under-graduate work (no matter how valid or relevant) may well not be considered, as HR departments can be notorious box-tickers! [*]
Personal Experience has shown that I've been required to complete probation at every permanent role I've had - even with 25+ years in the Big Wide World, of which 12 were "full time" freelance, and several others were/are part-time freelance.
Probation is a two-way process, which allows you to see if you fit into the company and its culture, as well as the company assessing you.
I certainly wouldn't take offence that you've been asked to undertake a probationary period... if they thought you were not up to the job, they wouldn't have offered you it!
[*] Off topic anecdote: in 2008, I was asked by the MD of my then main client to take on a full-time permanent role within the company. After some negotiation, we shook hands on a deal.
Then HR got involved, and amongst other things, I was required to submit two references (even though I'd been working with the company for several years).
My first two referees were rejected as being inappropriate - the Managing Director and the Engineering Director :) So I had to get two people I hadn't spoken with for nearly five years to act as referees...