yep, you have to remember that ARkefly (TUI Airlines Nederlands is you want to be picky) isn't actually Holland Excel.
Holand Excel closed down by their owners and TUI Airlines Nederlands was started up as a new company by TUI. The aircraft operated by TAN were previously operated by Holland EXcel, but it wasn't a simple TUI purchased the company, it was a new company, the leases were renegotiated, some of the staff were taken from Holland Excel but not all of them, and TAN didn't take over all of the flying that Holland Excel previous did, in the main it took over the TUI flying previously undertaken by Holland Excel.
TAN have has their problems, 3rd party maintenance providers causing significant damage to one aircraft during a major check, ground handlers marshalling an aircraft into a lamp stand as well as other issues with a major maintenance provder, but either way they're not the same airline as Holland Excel. TUI are lucky in that they have 7 airlines in the group (ok 8 at the moment til TOM and FCA merge) and a current fleet of 160 aircraft, which means one airline can often cover for another when it has operational issues, hence the TOM 767s covering a number of TAN flights over the last few months.
Three ageing and unique (to the TUI fleet) B763s doesn't help, although the engines on the TAN 763s are common to the B744 engines that Corsair operate.