Don’t know about Edinburgh, sorry, but they withdrew a lot of the UK lounges in the year or so after Emerald Airlines started, so maybe during 2022/2023. Hard to be sure as they removed lots from the website long before they actually withdrew access.

If you're thinking of a business class flight that connects via Dublin to the USA, the thing to watch for is Emerald Airlines - if it's a 3XXX flight number, you'll get zero recognition on that leg of the journey with the exception of Birmingham and Manchester.

If you're on an Aer Lingus prime flight, from most destinations you'll get lounge access and priority boarding.

It is what it is - Aer Lingus is only a full-service airline (barely) on TATL and is a value carrier to all other destinations. The variation in service to connecting business class TATL customers reflects that - from absolutely nothing in some cases to a seat in the front and free sandwich.

Technically all the info is on their website, but they don't really spell out what it really means for connecting business class passengers imho, so I can see why you're salty about it. Aer Lingus Business Class is usually a bargain where you can save €1000 or more that more than makes up for having to buy your own lunch at the outstations, but if you're a connecting passenger who paid a similar price to other airlines, it just feels like a pretty basic product.