I am jealous of the time you have been blessed to be a birder. I am about 6 years into birding at 74. My go to paper research books are The Crossley ID Guide for Raptors, The Kaufman Field Guide to Advanced Birding and Advanced Birding by Kenn Kaufman (Peterson Field Guides) but they are not used in the field not practical for me in the heat of battle
I use Merlin with the knowledge that it may only give me a starting point or be completely off. I use it after most birding trips and find it incorrect or inconclusive on many birds.
I have a hearing loss, since I was 16, totally gone above 9,000 hz and marginal above 8000 so birding by ear not very usefull for me much of the time. I do now have hearing aids that let me hear some birds, like Song Sparrows, if they are close enough. The first time I had the hearings aids in and could hear a song sparrow I was photographing it was an amazing experience.
I use cornell all about birds on my computer and have it on my phone but seldom use it in the field when birding.
As I have gained more experience I can ID many birds by field ID marks even in flight. When I get images downloaded on to my computer I can usually ID from Cornell All About birds if needed. My biiggest ID challenge is late summer molting adults and juvenile birds growing up.
At home my "paper" still comes out and I learn a bit more every birding day. I also have a couple of ornithologist friends that help out and I help them out with photographs.
My Ornitolgogist friends have edcuated me on why you need to be very judicious about using electronic calls for getting a bird photograph given the negative impact it can have on the birds especially if mutliple people are hitting them with calls in a day and day after day and they are being diverted from normal activities, like feeding