This type of cdv design with the square black font under the print was used by a number of photographers
in 1861 and possibly 1860 (Ralston & Sons, J. Bowman, MacNab). The drape on the floor behind the gentleman
probably conceals the stand of a head support, which was necessary with the long exposures required at this time.
The cdvs above come from the period before Stuart opened premises in Helensburgh, and one is dated to 1862. Again, the stand of a head support can be seen behind the gentleman.
These slightly later cards above, show that Stuart is now also established at Lomond street in Helensburgh. This card design was in use in 1864, and he is known to have been at that address in that year. The card on the left has been trimmed at the bottom, so may or may not have had the remark about duplicates. The line carrying the Helensburgh address on it is slightly askew, suggesting that it was added to an existing design, and thus that he had only recently set up here. The hair styles, partially concealing the ears, support a date in the early to mid 1860s.
In the cards above, Stuart has moved to a Charlotte street in Helensburgh, where he is known to have been in 1867, and indeed the second of these has probably come from there. But the card design is the same, so we are probably still in the later 1860s.
We see the name on the front of the cdv below, though Stuart has not yet got round to mentioning the Helensburgh location. This is a later 3/4 framing, and probably comes from the early 1870s, although the card is thinner than those above..
The two cdvs below have later types of design on the back, so are probably from the early 1870s, and indeed one example of the first is known dated 1872. The setting of the boy at the lectern looks earlier, however, and this could possibly be an earlier print re-photographed.