Section 8 - Letting Agents not able to provide evidence of landlord checks - ground 17

Possession - Section 8 and Section 21

Advise please: I have some self confessed hoarders in a property which was initially let by an agent. I have asked the agency for copies of the reference correspondence obtained from the past two landlords and to date have only been shown the computer screen stating yes to good paying tenants and no to issues. I understand that I can serve a 21 from the fourth month of occupancy however with the Covid Legislation changing it may be prudent to wait until the end of May. Or can I serve
a section 8 and should the agency be unable to produce the relevant checks were actually done would it be fair to say that any court costs would be down to them due to their failings under a section 8 ground 17. Or is that just a ground to issue the section 8, If at all? There are red flags all over the place and my gut feeling is that the tenants have been around this block a few times from refusing an inspection to rearranging and saying that wool will be pu away! (there are boxes everywhere and not one bit of kitchen surface can be seen for stuff, wife has anxiety and hoarding is due to mental health and liking stuff, I am being very pro - active in assisting the tenants but would like to get my ducks in a row knowledge wise. Thank you in advance. Jan