Calculate rolling adjusted date based on date from parent row - lag / recursion

Question

Given the data set below, I need to calculate a rolling AdjustedHireByDate. Each AdjustedHireByDate should be @NumWeeks weeks from the previous row's AdjustedHireByDate (if they have the same parent) unless the PreviousHireDate on the current row is not null. If PreviousHireDate is not null, use the PreviousHireDate to calculate the AdjustedHireByDate for the given row. This all stems from an initial parent record who's HireByDate does not change (unless it has a HireDate of course).

Sql Fiddle

-- INIT database
CREATE TABLE Vacancy 
(
    ParentID INT NOT NULL,
    PreviousID INT NOT NULL,
    CurrentID INT NOT NULL,
    PreviousHireByDate DATE NOT NULL,
    PreviousHireDate DATE NULL
);

INSERT INTO Vacancy (ParentID, PreviousID, CurrentID, PreviousHireByDate, PreviousHireDate) 
VALUES (3752, 3752, 3753, '2024-11-18', NULL),
       (3752, 3753, 3754, '2025-02-24', NULL),
       (3752, 3754, 3973, '2025-06-02', NULL),
       (3752, 3973, 4391, '2025-09-08', NULL),
       (3752, 4391, 4650, '2025-12-15', NULL),
       (3957, 3957, 3958, '2024-10-21', '2024-10-28'),
       (3957, 3958, 3959, '2025-02-02', NULL),
       (3957, 3959, 3960, '2025-06-23', NULL),
       (3957, 3960, 4146, '2025-09-15', '2025-08-04'),
       (3957, 4146, 4623, '2025-12-22', NULL);

ParentID	PreviousId	CurrentId	PreviousHireByDate	PreviousHireDate
3752	3752	3753	2024-11-18	NULL
3752	3753	3754	2025-02-24	NULL
3752	3754	3973	2025-06-02	NULL
3752	3973	4391	2025-09-08	NULL
3752	4391	4650	2025-12-15	NULL
3957	3957	3958	2024-10-28	2024-10-28
3957	3958	3959	2025-02-02	NULL
3957	3959	3960	2025-06-23	NULL
3957	3960	4146	2025-09-15	2025-08-04
3957	4146	4623	2025-12-22	NULL

Desired output given the above data set and using @NumWeeks = 2 (note this will usually be 8-24 weeks, but for simpler math/validation using a simpler number so the dates may seem to be getting adjusted more significantly than they will in practice.):

ParentID	PreviousId	CurrentId	PreviousHireByDate	PreviousHireDate	AdjustedHireByDate
3752	3752	3753	2024-11-18	NULL	2024-12-02
3752	3753	3754	2025-02-24	NULL	2024-12-16
3752	3754	3973	2025-06-02	NULL	2024-12-30
3752	3973	4391	2025-09-08	NULL	2025-01-13
3752	4391	4650	2025-12-15	NULL	2025-01-27
3957	3957	3958	2024-10-21	2024-10-28	2024-11-11
3957	3958	3959	2025-02-02	NULL	2024-11-25
3957	3959	3960	2025-06-23	NULL	2024-12-09
3957	3960	4146	2025-09-15	2025-08-04	2025-08-18
3957	4146	4623	2025-12-22	NULL	2025-09-01

Current select is

DECLARE @NumWeeks SMALLINT = 2;

WITH InitialHireByDate AS 
(
    SELECT 
        *, 
        CASE 
            WHEN ParentID = PreviousID 
                THEN COALESCE(PreviousHireDate, PreviousHireByDate) 
            ELSE NULL
        END AS AdjustedHireByDate 
    FROM 
        Vacancy
),
LaggedHireByDate AS 
(
    SELECT 
        ParentID,
        PreviousID,
        CurrentID,
        PreviousHireDate,
        PreviousHireByDate,
        DATEADD(WEEK, @NumWeeks, 
                COALESCE(PreviousHireDate,   
                         LAG(AdjustedHireByDate) OVER (PARTITION BY ParentID ORDER BY PreviousID ASC)
                        )) AS AdjustedHireByDate
    FROM 
        InitialHireByDate
)
SELECT * 
FROM LaggedHireByDate