Like the OP I managed to book my first flight with Norwegian from Gatwick to Palma (One Way) in June but without my flight accruing value to the Norwegian Reward scheme. This seemed to be because I was not logged in to my Norwegian Reward account before initiating the booking, even though I had already created a Norwegian Reward accounts. My second booking for a one way flight from Gatwick to Palma in September did track ok.
Confusingly my account page today for the Norwegian Rewards scheme says I have a Balance of 0 Cash Points and yet when I look at the flight booked on 24th Sept (it was actually for 29th Sept but the Reward scheme only seems to keep track of the date of flight booking and not the date of travel for some odd reason) it shows I have 0.21 CashPoints. So am I only shown as having a 0 Cash Points balance on the summary page because I do not yet have 1.00 worth of them yet? And is that 1.00 worth in NOK, EUR or GBP?
Either way this has to be the most ungenerous Rewards Scheme in history by an airline as Rewards seem to accrue only against flight value (I later added a hold bag 24 hours before the flight but no points have accrued in relation to that) and not add on options and at only a 1% level. So basically if you only travel on Norwegian's budget low priced flights it is usually going to take you 100 flights before you accrue enough Cash Points to take a free one. The only people for whom this will not be true may be business persons booking last minute at very high fares like 500 Euros return paid for by their business but who choose to carry out their later redemption activities on the lowest possible cost Norwegian flights. Passengers booking very expensive Norwegian Business fares may I suppose only need to take say four top price return flights at 500 EUR return (eight flights in total) before then then finally have 20EUR of Cash Points that they can use on one of Norwegian's cheapie one way fares.
However if you only ever book Norwegian cheapie fares at 21GBP one way or similar then the Rewards scheme is a waste of time as it will take 100 single or return journeys before you can book either one single or return free flight. Now forgive me for being cynical but I am sure Norwegian probably also have a way of expiring off the points as outdated or for inactivity etc before you are every likely to be in a position to book such a free flight.
In summary the Norwegian Rewards points are clearly only there to make passengers paying top business fares with Norwegian feel like they are getting something back (even though it is still only at a 1% Reward Rate of the fares they have paid). For everyone else booking cheap fares only with Norwegian their rewards scheme is more or less a total waste of time.