Don't feel guilty Ben10.
They don't do 2 year checks here either. You get a very brief questionnaire through the post which asks if you have any concerns in certain areas, but doesn't explain what might/should be a cause for concern. 
In fact, I had one through on Monday for dd (who is already 2.4 months old). I was furious a bit cross, as not only have they rezoned the HVs so we have been signed off by ours and put on the list for one at a different surgery - she has never once been in contact.
My old HV was fully aware that ds was going through assessment when she signed us off and being really supportive - even talking through and taking the time to understand my worries re delaying the MMR and making a note for them to stop inundating me with 'reminders'. She was such a great HV and I really miss her. We've been on the new HVs list for nearly 9 months now and haven't heard from her once. To me, having it in my records that I have one child with ASD, should flag up somewhere the need for a proper 2 yr check for dd - its no wonder so many children slip through the net at this age. 
That said, I don't think I am going to bother anyway, as lovely as she was, my previous hv knew less than me about ASD and early warning signs and I've yet to meet one personally that would be able to spot it at this age. (Of course I could be wrong and my new hv might be an expert - but how would I know?
)
Anyway, thankfully I have absolutely no concerns about dd and with her being number three - having one with dxd ASD and one with noticeable traits, but nowhere near enough for a dx - I feel far more confident of my own judgement this time round.
Like I said Ben10, try to put it out of your mind, we all have our lists of 'what ifs' and 'should haves', but really they are just wasted energy, which we could be using to help our dcs in the here and now, iyswim.