90 use is become MORE regular now - currently three on hire from FL and used most nights.
The impending arrival of Mk5s creates an INCREASE in the need to use 90s, not a decrease, as the 92s are being readied for the Mk5s. There's now 2x Class 92s set up for Mk5 ETS and being used for testing/training (014/023); plus 043 in Brush getting CAF mods; 3x 92s unavailable due to preparations for Mk5s = 3x 90s on-hire.
In addition, 92020 has just returned to full mainline action and 92006 will be emerging from Brush in the next month or so - both of which have CAF mods to work the Mk5s and will bolster the 92 Sleeper fleet in due course as the 90s roll-off (which will coincide with when the old stock is finally retired).
Similar scenario with the 73/9s - there's one or two being used currently for Mk5 testing, hence the 67 has been kept on hire to cover. When it's all Mk5s, there won't be any 73/9s tied up with Mk5 testing...