Yes, the serial number is on the right side of the receiver ring, barrel shank, inside the stock channel and under the bolt handle only. All other parts are unnumbered , different from Mausers. The Steyr factory serial number is not to be confused with the proofhouse ledger number stamped on M-Sch's until the late 1920s. FI 1618.27 means 1618th gun proofed in 1927. Here are my Mannlicher-Schoenauers sorted as to proofdates:
Model_________Caliber__________Serial#__Proof date as stamped
M1924________30-06_____________299____1618.27
M1925_________8x60 Magnum____3233_________34.
M1903________6.5x54__________23979_________36.
M1910_______9.5x57___________11400_________37.
M1950_________7x57____________3092_________51
M1950*______6.5x68___________22638_________57
*my 6.5x68 is marked " Mod.1950" on the receiver ring, though it is obviously a post-1952 action without clip guides, but with low bolt handle, side safety and dummy side plate inside stock to facilitate side-mounting a scope. Note that the post-war proofdates are above the stockline, visible without disassembly.
Those +- numbers, +-05 on your rifle, are apparently measurements to help fitting barrel to receiver . I have encountered them on prewar rifles, runnig from 05 to 2. These are on barrel and receiver, with a + on one and - on the other.