It might help to have more context from the rule
TheSYDTraveller was quoting, but is it possible that "RTG" is not an abbreviation (given everything's upper case anyway) but simply shorthand for ROUTING?
Fare rules often contain the words "PUBLISHED ROUTING" and/or "CONSTRUCTED ROUTING".
I've attached a snippet and bolded the RTG in question. You could be correct that it constructed routing but I can't say for certain as this does deviate from the more conventional routing rules.
SPK-SYD CXR-MH TUE 11JUN24 USD
THE FOLLOWING CARRIERS ALSO PUBLISH FARES SPK-SYD:
3U 9W AF AI BA BI BR CA CI CO CX CZ DL EK EY FJ GA GS HU HX JL
JO KA KE KL LH LO MF MI MK MU NH NZ OZ PG PR QF QR SB SQ TG TK
TN TR UA UK VA VN ZH
//SEE FQHELP FOR INFORMATION ABOUT THE NEW FARE DISPLAYS//
SURCHARGE FOR PAPER TICKET MAY BE ADDED WHEN ITIN PRICED
JPY CONVERTED TO USD USING BSR 1 JPY - 0.00658737 USD
MH-MHC/BUSSBASIC - BUSINESS BASIC
MH SPKSYD.EH 11JUN24 MPM 6447
V FARE BASIS BK FARE TRAVEL-TICKET AP MINMAX RTG
1 ZBS1YJP Z‡R 1825.00 ---- 7 3/12M EH01
2 ZBS1YJP Z‡R 1891.00 ---- 7 3/12M EH02
3 ZBS1YJP Z‡R 2058.00 ---- 7 3/12M EH03
4 ZBS1YJP Z‡R 2124.00 ---- 7 3/12M EH04
EH01* /WITHIN THE EASTERN HEMISPHERE/ CONSTRUCTED RTG
1. SPK-JL/MH-OSA-KUL-SYD
EH02* /WITHIN THE EASTERN HEMISPHERE/ CONSTRUCTED RTG
1. SPK-JL/MH-OSA-KUL-ADL-QF-SYD
Thanks for everyone's assistance!