Harry of Ciro's prints the Buck's Club London Side-Car as an equal-parts brandy, cointreau, and lemon drink.
Harry of Ciro's ABC of Mixing Cocktails by Harry of Ciro's (1923, p.77) — Buck's Club London
| 0.5 glass | lemon juice — Lemon Juice | acid |
| 0.5 glass | brandy | base |
| 0.5 glass | Cointreau — Cointreau (Triple sec) | base |
This matters because it captures the Buck's Club London Side-Car in a 1923 source rather than only later standardizations.
The source presents it as a plain shaken equal-parts sour without extra decoration.
About Town Cocktail Book by Joe Fitchett (1925, p.22) — Vancouver Club
| 50 percent | brandy | base |
| 20 percent | lemon juice — Lemon Juice | base |
| 30 percent | Cointreau | other |
This matters because it preserves a Vancouver Club Side-Car checkpoint in percentage notation.
L'Art du Shaker by Dominique Migliorero (1925, p.62)
| 0.33 part | cognac — Cognac | base |
| 0.33 part | lemon juice — Lemon juice | base |
| 0.33 part | Cointreau | other |
The source attributes this to Mac Garry, London.
Barflies and Cocktails by Harry McElhone and Wynn (1927, p.72) — MacGarry / Buck's Club
| 0.33 part | lemon juice — Lemon Juice | acid |
| 0.33 part | brandy | base |
| 0.33 part | Cointreau — Cointreau (Triple Sec) | base |
This matters because it preserves one of McElhone's central Side-Car witnesses with explicit Buck's Club attribution.
Cocktails by Pedro Chicote (1928, p.221) — Cognac and Cointreau
| 0.5 copita | cognac — Conac | base |
| 2 coffee spoons | lemon juice — Jugo de limon | base |
| 0.5 copita | Cointreau | other |
Ice: Cracked ice
This matters because it gives Chicote a clear Side-Car checkpoint inside the Madrid hotel-bar layer.
See also: Orange Cocktail, Taxi Cocktail