With Silver and Gold the DLC is free until you stop subscribing, if you stop then it gets disabled, you can however purchase normally if you prefer or before cancelling Silver in which case it won't disappear or if you start subscribing again later it all comes back again.
All very confusing when confronted with all the choices.
Should say that Platinum is apparently according to N3V the latest version of Trainz and a separate install not an upgrade, so it looks to me as if Normal non subscription TRS19 will not have any more updates after they fix the pause issue with it!
You can of course have Non sub TRS19 and Silver or Platinum and Silver, if you already have the non sub TRS19 and got Platinum you would have two separate installs, add Silver and it covers both though for the DLC and the FCT.
Plus and Gold Plus gets even more confusing!