business_cycle: three statements the World Bank data do not bear out #851

Found on 2026-09-30 while porting lectures/business_cycle.md to lecture-wasm (QuantEcon/lecture-wasm#85), which reads the same World Bank series from cached snapshots. All three are prose or caption problems in intro main (901462c). The code and figures are fine.

1. Argentina in the 1970s (line 320). The lecture says "Argentina's growth rate did not fall during the two developed economy recessions in the 1970s and 1990s." The figure shades 1973–1975 and 1990–1992. World Bank NY.GDP.MKTP.KD.ZG for Argentina is 2.81% in 1973, 5.53% in 1974 and −0.03% in 1975 (−2.02% in 1976), so growth did fall in the 1970s band. In the 1990s band it rose (−2.47% in 1990, 9.13% in 1991, 7.94% in 1992), so that half holds.
2. UK credit "from 1970" (line 754). The lecture says "The following graph shows the domestic credit to the private sector as a percentage of GDP by banks from 1970 to the present in the UK." The series starts in 1960, at 17.34% of GDP (19.82% in 1970), and the figure plots it from 1960.
3. "by banks" (lines 751 and 754, and the caption at line 760). The code reads FS.AST.PRVT.GD.ZS, which the World Bank names "Domestic credit to private sector (% of GDP)", covering credit from all financial corporations. The "by banks" series is FD.AST.PRVT.GD.ZS, "Domestic credit to private sector by banks (% of GDP)". Either the text and caption drop "by banks", or the code reads FD.AST.PRVT.GD.ZS.

The values come from the World Bank API as cached in QuantEcon/data-lectures (gdp_growth_annual.csv and private_credit_to_gdp.csv). On 2026-09-30 they were identical to live wbgapi reads. The series names come from api.worldbank.org/v2/indicator/<id>.

QuantEcon/lecture-wasm#85 carries the same text unchanged, so a fix here should be mirrored there.