Douglas744 is correct with his explanations.
However, no TO/GA mode is not really a big issue. Your hands should always follow the throttles anyhow and move them forward on a GA. ('Basic airmanship).
It is not possible to overboost the engines if the EEC's are operative.
1 click of the TOGA: 2000'/min. ROC, annunciated as THR ( the thrust needed for a requested vertical profile)
Second click: Full GA thrust, Annunciated as THR REF ( all available thrust)
LNAV or HDG SEL at 400'
VNAV at 1000' ( Boeing procedures)
Some more observations:
TO/GA will remain armed until 2 seconds after 5ft. RA ( some manuals state 2 sec. after touchdown)
As I mentioned before, in case of no auto retard of the AFDS at 25ft. RA, the aircraft will not touch down and fly happily a couple of feet high With Vref along the runway.