The “Transitional” period is the era of Conn saxophones where Conn was switching back to left-side bell keys. They’re also notable for having a beautiful, art-deco-style engraving.
Other than the engraving, the 4M curved soprano and 8M C melody tenor did not change at all during the “Transitional” period.
The straight soprano underwent a massive bore redesign in 1928, where the overall length of the horn grew by (IIRC) a half inch. This design allegedly made for better intonation, but today it also made for a lot of folks confusing the 18M with an A soprano, which (sadly) never made it into production.
“Transitional” model New Wonder saxophones in finishes other than gold plate have a standard engraving. It’s not custom, nor as elaborate as what’s on their gold-plated brethren, but it’s still beautiful.
As mentioned above, the 8M C Melody Tenor did not change at all during the “Transitional” period, other than with the engraving. The popularity of the C Melody was getting fairly low by the 1930s. There were some later US-made horns, though.
The “Transitional” period for Conn refers to the period between roughly 1930 and 1935 where Conn was making a variety of key and bore changes, one of the more obvious changes is a switch back to single-side bell keys on the alto. The era ended when the tenor gained single-side bell keys, at approximately serial number 262500.
It’s not only possible, but probable that there are “Transitional”-engraved horns of other pitches than those mentioned above, including the 16V Eb contrabass Sarrusophone (Conn’s Eb contrabass saxophone equivalent). I’ve just not seen them. A Conn Bb bass saxophone with “Transitional” engraving would be absolutely epic!