Not sure what you mean by cutting the trunk - sounds rather drastic! All you need to do is gently scratch a very small bit of bark to see if its green underneath. It is under enough stress being moved without adding to it by
"cutting the bark", which you should not do at all in any case. it just adds more stress to what for the treelets is already a stressful situation.But it is wise with a newly planted tree to leave it rather longer before trying to do anything, as moving is rather a shock for them and may slightly delay them coming into leaf. Are you sure that the horse manure was as well rotted as you thought it was?
You were right to add some loam because beech normally thrives in damp leafy soil in woodland. In fact leaf mould might have been a better bet than manure but never mind.I have never seen beech on sandy soil. With any new planting you should get the soil right, keep it moist, as you did, and then Have Patience, which you did not do! You cannot rush gardening.It will take a long time for you to see the beautiful mature beeches in their full glory. You put in good plants, you added good stuff to the planting hole, you kept the ground moist. Now you must WAIT. You cannot rush nature. This year your saplings will be busy making roots - don't dig them up to check!

Thank you for your kind reply. By trunk I meant the main central stem, I cut this towards the tip firstly to stop the apical dominance allowing strong side shoots to develop I wanted this to be a thick hedge rather than individual trees, this then allowed me to check that the stem was still showing green . I've been v lucky in that my neighbours who are not gardeners have 3 ton of 5 to 10 year old horse manure which is a very deep colour and holds together beautifully before being broken up by myself. This has allowed me to garden here in Lincolnshire on v Sandy soil. I've managed by digging in this combination to cultivate the front in relative shade. I've now turned my attention to the rear which unfortunately can be baked in sun. Seems I've made an error I thought the atropurpurea required full sun to maintain that beautiful deep colour. I will leave well alone now but move late Autumn to shade and enjoy them there instead. Laurel seems to survive around these parts but I wanted to try something else. I'm trying to plant staggered Hedges to break up the wind. Thanks again for your advice much appreciated.