So far my Xiaomi Mi A2 Lite has received Bi-monthly Updates on its Android One OS

Responses to date confirm my opinion that Android 1 is a program controlled by the hardware vendors (Nokia in my case) and not Google.  In this respect there is no difference in levels of Android maintenance and support - Android supplied through the Android 1 program is supported (or not) in exactly the same way non-Android-1 versions.  You are simply at the mercy of your hardware vendor and if they decide to no longer make updates available you have no recourse.

Before anyone leaps in with CGA references, the CGA does not apply to software release maintenance.  My phone works as it should but I am concerned at the potential vulnerability to issues (not just security-related) fixed in a release that is not available to my 6-month-old handset because it is being withheld by the phone manufacturer.

I have just received a maintenance update that also includes the June Security Update.

However I cannot be certain why the update came through.  Was it because I was VPN-connected through a Hong Kong based server or would the update have come through anyway? I am using NordVPN and 7 days into a 7 day free trial (now cancelled).  Nokia support told me that based on the SIM1 IMEI my handset was exported to Hong Kong (I bought it from Parallel Imports).  Using the VPN delivered significantly slower data (as expected) and no other obvious benefit so I no longer need it and only tried it because it was a no-cost option.

I am happy though that updates are still being received.

I too am receiving that update on my Nokia 7 Plus (TA-1055).

I'm on Spark, and phone was purchased through Spark.

1st update since April.

I also received the "1 June 2019" update on my Nokia 6.1 overnight, and I am not connected to any VPNs or fancy stuff like that, so it's just been distributed through the Spark network. I bought the phone off Spark too, BTW.

I'd guess that your complaining about it on the incredibly-well-recommended GeekZone sparked [cough] someone into action and caused the pipes to get unblocked.
[I think I'm joking, but ...]

Well look at that, my 6.1 is also now busy installing the V3.54E update for Pie.

I bought mine through an independent retailer (NZ new stock, not parallel imported) and connected to 2Degrees so it's not a "Spark thing".

MackinNZ:

 

I too am receiving that update on my Nokia 7 Plus (TA-1055).

 

I'm on Spark, and phone was purchased through Spark.

 

1st update since April.

 

Same with Wife's  7 Plus. 

Good news Nokia users, Android 10 looks like it'll be pushed out to most Nokia's running Android One over the next few months.  My 6.1 will likely be Q1 2020 (or Q4 this year depending on where you read it).

https://www.androidcentral.com/will-my-phone-get-android-10#nokia