Newbie..any Help Appreciated (Two Notes, Same Serial Number)

Hi

I'm new to collecting banknotes and sticking with British currency for now. I've collected around 20 notes to date from a T24 to some of the new polymer £5. Reason for searching down a forum is to ask for help with the following:

Around three weeks ago I picked up a Lowther £10, a low number AA01 and today, from a different respectable dealer, purchased a Lowther £20, another AA01 and to my delight both have the same low serial number. So I have two notes of different denominations with exactly the same first series number in UNC condition.

While this seems a rare occurance to me it may well not be and can anyone advise on how valuable this makes the 'pair'? Duggleby's 9th lists both AA01s at £60 each in UNC condition and I'm guessing each alone would attract slightly more interest due to a low four figure AA01 serial number.

Any educated guesses at a combined value given the information provided would be extremely helpful.

Thanks for any help and apologies if this is basic and much more common than I think.

Steve