Hello and welcome! I've seen your post on the other old thread of someone else's, in which you gave a bit more detail: www.mumsnet.com/Talk/home_ed/1260433-letter-received-from-elective-home-education-co-ordinator
No, there is no legal requirement to register or fill in any forms. Many LAs make up their own policies, but if they have no force in law then you don't have to comply. If I were you, I would be wary of your particular LA as they are either clueless or trying deliberately to mislead you - both of these are common problems with LAs.
Bear in mind that the ultimate sanction they have against you, if they had reason to believe you weren't giving your son a suitable education, would be to order him to school. They cannot issue a School Attendance Order until they have asked you to supply information, and then if they still aren't happy they must lay out their concerns and give you a chance to address them. Then a judge would have to agree with them. This process takes a while. Since you plan to send him to school in the autumn anyway, it isn't something you need to worry about much.
Having said that, you could probably do without the hassle of being threatened with court, and you want to retain the option to home educate later if you change your mind about secondary school or if your son tries it and doesn't thrive there. For this reason, it would be wise to comply with any requests they make when those requests do have a legal basis. If they ask you for anything which they don't have a right to, you can write to them asking them to quote the law which says you have to do it. Since there is no such law, they should drop it then.
The usual advice given for dealing with LAs is to ask them to keep everything in writing, decline any offers of home visits, and always respond to any communications from them - either by complying with what they want, asking for clarification, or challenging them. If you ignore them altogether, then they may decide you aren't engaging and escalate toward legal action.
Your son's attendance history has no bearing on the education you are now providing, and isn't relevant. In practice you may find that your LA targets you because they may imagine you removed him from school purely to avoid a truancy prosecution and that you have no genuine intention of home educating him. But that doesn't affect the legal situation.
What is ESBASS?