According to this document, each strand of 12 LED lamps draws 36 VA which converts to 3 amps. A 200 watt transformer has an output of about 16 amps at 12 volts, so it should be able to handle about five strands or 60 bulbs, total.

Typically, you should check with the manufacturer of the transformer to verify what % of the rated load they recommend using. A lot of manufacturers typically don't recommend fully-loading a unit; we recommend using 80% for ours. With that number in hand, divide it by the wattage consumption of a single one of the hardscape lights; you will then know the total amount of lights you can add.

A quick google search brought up the operator's manual for a 'Low-Voltage 200-Watt Landscape Transformer'. Just to verify, it said: "Be sure that the total cumulative wattage of all 12 volt fixtures connected to the transformer is equal to or less than 200 watts." I wouldn't know the wattage of your hardscape lights without knowing a model though.

https://www.uniquelighting.com/en/fixtures/hardscape-lights/iso