Question on boundary line adjustments

We could tell because it would be recorded something like...

Lot 1 of New Plan 123 being Lot 1 and Part Lot 2 Old plan 789

you took two feet off of Lot 2 and added that to Lot 1

Sounds like you know where the line between the two lots is, so moving the line means they are no longer the lot one and lot two from the original plat.

If this were a record plat we would show the new lots, dashed old line and it would be lot1a and lot2a on a new revised plat recorded in land records, titled Revised Plat of ....

A better example.  Hank Smith owns Lots 1-12.  The appraiser views all of that being Parcel #97-062-43-1298-83-001 He hires you to create the following tracts: All of Lot 1, all of Lot 2 and Lot 3, less the east two feet thereof.  The east two feet of Lot 3, all of Lot 4, all of Lot 5 and Lot 6, less the east four feet thereof.  The east four feet of Lot 6, all of Lot 7, all of Lot 8 and Lot 9, less the east six feet thereof.

That leaves Smith with the east six feet of Lot 9 and all of Lots 10-12.

There are now only four owners for what was 12 lots.  Are these new lots identified as Lots 1,2,3,4?  Are they now Lot 1, Lot 4, Lot 7 and Lot 10?  What government office holds the key information for you to know at a glance that Lot 1 is not really the platted Lot 1?  Especially in a non-recording State?

In my area, we apply the original lot number or part there of as a separate piece of ownership.  The first tract above consists of three separate tracts and any one of them may be conveyed to someone else.  The second tract above consists of four separate tracts and any one of them may be conveyed to someone else.

Posted by: @holy-cow

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How do you know they have changed?

In Oregon:

1. There will be a Record of Survey detailing the change in the County Surveyors records.
2. There will be new deeds recorded with the updated descriptions. Which would be "Lot 1, TOGETHER WITH the east 2.00 feet of Lot 2" and "Lot 2, Except the east 2.00 feet thereof". 
3. The change would show up on the tax assessors mapping.

Other places maybe the process is not so formalized. But there must always be a recorded deed for the exchange parcel at least. Which makes a good argument for making a title report a routine get before doing a boundary.

Posted by: @joe-ferg

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In my area it would be a Replat of Lots 1 and 2 Blk X "Subdivision Name". The new pieces would be Parcels 1 and 2. New descrptions would read Parcel 1 (or 2) of of Partition Plat 2026-xxx. All directions and dimensions would be based on the new Plat.

This would be an alternate approach in Oregon.

In my area it would be a Replat of Lots 1 and 2 Blk X "Subdivision Name". The new pieces would be Parcels 1 and 2. New descrptions would read Parcel 1 (or 2) of of Partition Plat 2026-xxx. All directions and dimensions would be based on the new Plat.

I once had an adverse possession case in a subdivision/re-plat. The original subdivision name was Lake Sail-Em II. About half the lot owners didn't like the name and joined together in a new subdivision named Pebble Lake. The new subdivision used all the lot dimensions as the original but the Lot numbers were totally different. Tax parcels starting with 173 are still in Lake Sail-Em, parcels starting with 232 are in Pebble Lake.

Unless there was an over-arching reason to aggregate the lots into four distinct tracts, I would do the amended plat, showing the retracement of all 12 lots with the adjusted boundaries on lots 2a, 3a, 6a, 7a, 9a, &10a. Shown as the amended plat of lots 1-12, Block “#”, whatever subdivision, city of xxx, STR, P. M. , M. xxx county, MT. 
Property lines are $$$$$ to create, so don’t expunge them unless necessary. 

Thanks to all of you who replied to my questions.

I'm surprised that no one brought up the subject of Covenants to the original subdivision.
Covenants run with the land and are not extinguished by changing lot lines or re-plating.
One should first check to see if the Covenants would be violated by the action of boundary changes. Consideration should be given to how HOA dues would be paid by the changed properties.

@holy-cow 

In WA, you do a Boundary Line Adjustment, which is a separate (reviewed) process, essentially this is an exception to the platting law. The requirements are different in each jurisdiction if they have created a separate BLA Ordinance. If they have not, there is no set way that the revised lot layout is named. In some counties, they call them Resulting Lot A or such, keeping the same name but always with the "Resulting" prefix. In more sane jurisdictions, they require you to rename the lots entirely. If it was Lot 1, 2, etc, then you name them Lot A, B, C. So Lots 1 through 12 would become (in your example) Lots A, B, C, & D of BLA XXXX.

The previous Plat is not the legal description anymore, except that some people will make (or be forced to make) the legal description be the underlying lots and say also known as...which I extremely dislike because verbose legal descriptions when there is an underlying plat (the BLA in this case) is tiresome.